You could use some of that RAM to create a RAM disk. There are commands that you can run from terminal or get some 3rd party GUI tool that allows you to do the same.
However, there's a huge difference between SSDs and RAM disk. RAM is volatile, SSDs are not. If your computer suddenly loses power, crashes, hangs or reboots, everything that was in RAM and on your RAM disk will be lost. Obviously the same will not happen with SSDs.
Having said that, you might not realize it, but OSX already does something similar to what you are thinking of doing. All that free memory in your computer is not being wasted. OSX automatically uses it as a cache. Whatever your computer reads, gets cached in free RAM. The next time you need that file, it'll be available to you nearly instantly.
Take a look at this answer, it's much more eloquent. Isn't Inactive memory a waste of resources?